A. Field of the Invention
The present invention relates to an UTOPIA switching device for a braodband switching system, especially to a stackable UTOPIA switching device (USD) for an ATM switch which can be arranged as a tree-like hierarchy for connecting to multiple digital subscriber lines (DSL).
B. Description of the Prior Art
With the advantages of high transmission speed and stable QoS, Asynchronous Transfer Mode (ATM) backbone has been a promising solution for high bandwidth transmission, such as asymmetrical digital subscriber line (ADSL) or Very high speed Digital Subscriber Line (VDSL). A conventional ATM switch 11 usually resides in a distribution point 10 of an ATM network system, such as a central office of a local telephone service provider, as illustrated in FIG. 1. The ATM switch 11 will transmit data to/from the user""s terminal 15 via the ATM backbone 16 from/to the ATM networks 17. The user""s terminal 15, usually referred to as customer premise equipment (CPE), has a point-to-point connection to the user""s premises ADSL MODEM 13 via the twisted copper wire pair customer line 14. Each ADSL MODEM 13 has a point-to-point connection to a high speed digital port 12 of an ATM switch 11. Since a high speed digital port 12 of an ATM switch 11 is very expensive and each digital port 12 is dedicated to an ADSL line, it makes the entire ATM switch 11 very expensive.
Moreover, the architecture of an ATM switch 11 is based on a fully-connected topology or a bus-like topology. The switch circuit for supporting fully-connected topology is complicated and expensive, especially when the number of ADSL users increases. The current technology of a switch circuit for supporting bus-line topology, on the other hand, can connect to 16 ADSL lines at the most, which is not enough for a large network system.
Accordingly, it is a primary object of the present invention to provide a stackable UTOPIA Switching device for the ATM switch which is easy to implement and can be arranged in a tree-like hierarchy for connecting to multiple ADSL lines, thereby to reduce the cost of an ATM switch.
It is another object of the present invention to provide a stackable switching device for an ATM switch which can be easily adapted to devices that supports UTOPIA interfaces.
In accordance with the present invention, the preferred embodiment of the present invention mainly includes a stackable UTOPIA switching device for use in an Asynchronous Transfer Mode switch. The inventive UTOPIA switching device can be easily arranged in a tree-like hierarchy to connect to multiple ADSL lines. A single UTOPIA switching device can connect to 4 ADSL transceivers. The UTOPIA switching device comprises an Up-link end and a down-link end. The down-link end can connect to 31 slave multiplexers or physical layers at the most. The up-link end can connect to a master USD or a slave USD. Both the up-link end and the down-link end have three input queues and one output queue for buffering the ATM cells. The ATM cells are buffered in the three input queues and the output queues in an order controlled by a priority queuing logic circuit. Additionally, a translation RAM can be added for looking up a new VCI/VPI in a table to replace the VCI/VPI field in the header of the cells. With the stackable architecture and the simplicity in the circuit design, the cost on the hardware-level implementation of an ATM switch can be successfully reduced.